1. Field of the Invention
The invention relates generally to Serially Attached Small Computer System Interface (“SAS”) devices and more specifically relates to apparatus and methods to test a characteristic of a SAS cable.
2. Discussion of Related Art
It is generally known in the computing industry that a peripheral interface circuit is coupled with a processor to provide I/O interfacing to peripheral devices by the processor. One common peripheral interface utilized for coupling peripheral devices to a processor is the SAS interface. SAS comprises a family of standards for coupling high speed peripheral devices (including storage devices) to computing systems or processors. Many details of the SAS family of standards may be found at www.t10.org. For example, many present-day high performance disk drives utilize the SAS family of standards to permit high-speed exchange of information with the computing systems or processors through appropriate high speed SAS links.
A SAS cable supports one or more SAS links between ports of SAS devices. A single port SAS cable supports one SAS link between a port pair, and a wide port SAS cable supports multiple SAS links between multiple port pairs. For brevity, a group of wires of a SAS cable that support a SAS link will be referred to as a “port” of the SAS cable. Because a wide port SAS cable has multiple groups of wires that support multiple links, the wide port SAS cable may be referred to herein as having multiple “ports.”
The SAS family of standards defines many different types of SAS cable connectors. Especially in a factory and/or laboratory environment, a wide port SAS cable can also have a wide variety of mappings from ports at one end of the wide port SAS cable to ports at another end. Given a particular port at one end of a SAS cable that couples to the particular port's respective port at another end of the SAS cable (i.e., the particular port “maps” to the respective port), there can also be many ways that wires of the particular port can be connected to wires of the respective port.
More specifically, a port of the SAS cable comprises a positive transmit (“TX+”) wire, a negative transmit (“TX−”) wire, a positive receive (“RX+”) wire, and a negative receive (“RX−”) wire. The transmit pair of the port at one end of the SAS cable can be connected to the transmit pair of the respective port at another end of the SAS cable. But the transmit pair at one end can also be connected to the receive pair at another end for a crossover port of the cable. The positive TX+ wire at one end can be connected to either the positive TX+ or RX+ wire at another end. But the positive TX+ wire at one end can also be connected to either the negative TX− or RX− wire at another end so that the polarity of the transmit wires is inverted. Similarly, the polarity of the receive wires can also be inverted independently of whether the polarity of the transmit wires is inverted or not.
As presently practiced, the wide variety of SAS cables are labeled and/or placed among like SAS cables in storage, and thus manually sorted and organized to define the cabling configuration. However, it has become very difficult to maintain an environment where many types of SAS cables are present because many SAS cables are labeled with insufficient information, labels may be removed, or the SAS cables may be misplaced in the wrong storage location. Meanwhile, many SAS cables are compatible with the Serial Advanced Technology Attachment (“SATA”) standard, further complicating the variety of cables that are available.
Thus it is an ongoing challenge to reliably and readily determine configuration characteristic characteristics of SAS and SATA cables.